This is a continuation-in-part of application Ser. No. 525,446 filed May 18, 1990 and now abandoned.
The present invention relates to emulsion type cold rolling oils used in a process for cold rolling of steel sheets.
In cold rolling of steel sheets, a fluid dispersion (called a "coolant liquid") which is prepared by emulsifying and dispersing a cold rolling oil in hot water at a concentration of 1-10% is usually employed by circularly jetting the same for cooling the heat generated at the time of working the steel sheets and supplying lubricating oil to the rolling rolls and steel sheets.
The cold rolling oil is a composition obtained by incorporating an oiliness improver, an extreme-pressure additive and an emulsifying agent for emulsifying and dispersing a basic oil such as animal, vegetable and mineral oils, or various synthetic esters and the mixtures thereof obtained from two or more of these basic oil components.
The adhesion (plate-out) of a lubricating oil to steel sheets or rolling oils is significantly affected by the emulsified and dispersed state of the cold rolling oil. In general, a larger diameter of the emulsified and dispersed particles brings about the better plate-out so that lubricity is elevated. Furthermore, in rolling, stability in lubrication is important because variation in lubricity interferes with the rolling operation. However, there is a tendency that the emulsified and dispersed state of the cold rolling oil varies during storage of the coolant liquid in a coolant tank and circular use thereof, so that it is difficult to maintain a constant emulsified and dispersed state. For this reason, the lubricity varies and it will seriously interfere with working stability.
One of the reasons for variation with time in emulsification and dispersion is due to particle size growth as a result of coalescence of dispersed particles of lubricating oil, and another is that emulsification and dispersibility are affected adversely by inclusion of the iron powder produced at the time of rolling and working the iron sheets. While a cold rolling oil which has been emulsified and dispersed maintains particles having a comparatively uniform particle diameter which is well-balanced by its stirring condition in the early stage of the dispersion, the particle diameter distribution gradually covers over a wide range from small to large particles as a result of coalescence and destruction of the particles. Furthermore, as a consequence of inclusion of iron powder, coalescence of dispersed particles occurs, whereby particles having larger particle diameters are produced. Such large particle diameter lubricating oil particles float easily in the coolant liquid tank, so that they float or are caught by the coolant liquid dependent upon changes in the stirring conditions. Thus, the distribution of dispersed particle diameters of the lubricating oil in the coolant liquid to be supplied to rolls or rolling steel sheets fluctuates As a result, its plate-out changes thereby to bring about variation in lubrication.
In order to avoid the phenomenon described above, the type, addition amount and the like of emulsifying and dispersing agents to be incorporated with a cold rolling oil has been studied Heretofore, a nonionic emulsifier having a molecular weight of 1000 or less has been used as an emulsifying and dispersing agent to be incorporated with a cold rolling oil for steel sheets. Recently, the use of water-soluble cationic high molecular compounds has also been studied and a part of which has been put to practical use for the sake of improving stability with time in respect of an emulsified and dispersed state. However, it is difficult to solve the problems as described above by the use of the nonionic emulsifier as previously mentioned herein. On one hand, while the stability with time is remarkably improved in respect of the emulsified and dispersed state in cases where a water-soluble cationic high molecular compound is used, such stability with time is easily influenced by water quality such as pH, hardness, components and the like of the water used because the emulsifier is cationic, on the other hand. Accordingly, water quality control is required and in addition, there arises another problem that since a water-soluble cationic high polymer exhibits no oil solubility, the cold rolling oil becomes a two-part liquid system so that its emulsifying and dispersing operability is poor.
In recent years, improvements in operating efficiency have been promoted by increase of rolling speed and draft, so that increasingly better lubricity and its stability with time are required for a cold rolling oil. In order to comply with such requirements, elevations in plate-out of a coolant liquid and stability of an emulsified and dispersed state are necessary.